About the Course
It's been really good! E&M is one of those subjects with a lot of free time. For many E&Mers pursuing a career in finance, this is really important - it gives you the ability to concentrate on applications and learning outside of the classroom. I would encourage them to take the chance to join professional societies (and also fun ones too), and to absorb knowledge as much as possible from seniors and peers. Often, forming close relationships will help with learning, and these relationships also carry-on far into the future.
E&M, by name, has two components. It's really nice that you've got the chance to take the subjects of your choosing: do take first-year as an opportunity to get a feel for what those subjects will feel like when you're studying them in much greater depth.
The Application Process
I think that the TSA formed a significant basis for the entire assessment of candidates. Getting a good score on the TSA, while not everything, can greatly increase a candidate's profile. For E&M, the TSA has changed since my time, so essays are no longer required. For the problem solving and critical thinking sections, I would advise that candidates apply logic in a structured and consistent manner. Heading into the interview, I would advise candidates to be calm and enjoy the process. Interviewers at Oxford aim to judge a candidate's potential at their best, and so they too want you to succeed. They will provide guidance mid-interview, so make sure you're receptive to feedback!